text: * [https://www.brenda-enzymes.org/ontology.php?ontology_id=3 BTO (BRENDA Tissue Ontology)]
  * [http://www.brenda-enzymes.org/ontology.php BRENDA Ontology Explorer]
  * [https://web.archive.org/web/20150506193454/http://www.brenda-enzymes.org/ BRENDA-website]
  * [http://www.enzyme-database.org/index.php ExplorEnz – Enzyme Nomenclature]
  * [http://www.obofoundry.org/ontology/bto.html Obofoundry]
  * [http://geneontology.org/ Gene Ontology Consortium]
  * [https://www.ebi.ac.uk/ols/ontologies/bto EBI-EMBL]
  * [http://bioportal.bioontology.org/ontologies/BTO Bioportal des National Center for Biomedical Ontology, Stanford, USA]